In the present time of pursuing fuel economy and fuel efficiency, one of the ways for effectively increasing the engine efficiency is to control the engine's valve timing. Electromagnetic valve mechanism has been developed to enable effective control of the valve timing. That is, the use of an electromagnetic valve mechanism in place of the conventional camshaft would bring the possibility of fully variable valve timing.
However, the conventional electromagnetic valve mechanisms have the following problems:
(1) Consuming relatively high energy: The conventional electromagnetic valve mechanism without permanent magnet requires additional energy to maintain the valve in a fully opened or a fully closed position, which results in consumption of extra energy.
(2) Requiring starting current: The armature in the conventional electromagnetic valve mechanisms is located at a middle position in a balanced state before the engine is started. Thus, a pilot current must be supplied for bringing the armature to the fully closed position before the engine is started. By doing this, a large quantity of energy will be consumed.
(3) Causing demagnetization of permanent magnet: While the conventional electromagnetic valve mechanism developed at a later stage is able to provide a force for maintaining the valve at the fully opened or fully closed position by applying a current to the electromagnetic coil for the same to produce a magnetic force opposite to and accordingly offsetting the force of the permanent magnet, so that the valve is released and can be actuated. However, with this design, the electromagnetic flux will pass through the permanent magnet in a reverse direction, which will cause demagnetization of the permanent magnet, resulting in lowered force of the permanent magnet.
(4) Causing uneven wear of valve: When the engine operates, the conventional cam-driven valves also rotate. During the rotation, the valve will contact with the valve seat to cause collision and wear. In addition, in the most of conventional electromagnetic valve mechanisms, the armature thereof is cubic in shape and therefore fails to rotate along with the rotating engine. This design not only causes uneven wear of the valve, but also the collision of the armature with the wall of the electromagnetic valve structure. As a result, the electromagnetic valve mechanism will become damaged after being used over a long time.
(5) Having a relatively large mechanism volume: To provide large magnetic force for moving the valve, the conventional electromagnetic valve mechanism includes a solenoid valve coil of a relatively large volume, which causes increased difficulty in mounting the large electromagnetic valve mechanism on top of the engine's cylinder head.
(6) Having a magnetizable block with relative small magnetic attraction to the armature before contacting with the latter: Due to the magnetic circuit design thereof, the conventional permanent-magnet electromagnetic valve mechanism has the problem of a relatively small magnetic attraction of the magnetizable block to the armature before the magnetizable block is in contact with the armature. Thus, in the event of any change in the system resistance, a system failure might occur.
(7) Having low system robustness and small variable operating ranges for parameters: In the event of changes in system parameters, such as demagnetization of the permanent magnet and degraded magnetic force lower than the initially designed magnetic force, the system would not be able to magnetically attract the armature and become failed without the ability of operating normally.
It is therefore desirable to develop an improved electromagnetic valve mechanism so as to achieve the purposes of lowered energy consumption, reduced overall mechanism volume, providing demagnetization-protection for permanent magnets, and enhanced valve performance.